24 Global Ecology

Global Biogeochemical Cycles Atmospheric CO 2 affects pH of the oceans by diffusing in and forming carbonic acid.

Figure 24.4 A FACE Experiment

Global Biogeochemical Cycles Concentration of CO 2 and CH 4 can be measured in tiny bubbles preserved in polar ice. The concentrations are correlated with glacial–interglacial cycles. Lowest concentrations correlate with glacial periods.

Figure 24.5 Temporal Changes in Atmospheric CO 2 and CH 4

Global Climate Change Climate change refers to directional change in climate over a period of several decades. Average global surface temperature increased 0.6°C (± 0.2°C) during the 20 th century. Concept 24.2: Earth is warming at an unprecedented rate due to anthropogenic emissions of greenhouse gases.

Global Climate Change Weather is the current state of the atmosphere. Climate is the long term description of weather, including average conditions and the full range of variation. Climatic variation occurs at a multitude of time scales—from daily and seasonal to decadal.

Figure A Changes in Global Temperature and Precipitation

Figure B Changes in Global Temperature and Precipitation

Figure C Changes in Global Temperature and Precipitation

Global Climate Change Greenhouse effect—warming of Earth by atmospheric absorption and reradiation of infrared radiation emitted by Earth’s surface. This is due to greenhouse gases in the atmosphere, primarily water vapor, CO 2, CH 4, and N 2 O.

Figure 2.4 Earth’s Radiation Balance

Figure Increases in Greenhouse Gases

Global Climate Change The Intergovernmental Panel on Climate Change (IPCC) was established in Experts in atmospheric science and economics from around the world.

Figure Contributors to Global Temperature Change (Part 3)

Global Climate Change IPCC’s models project a1.8°C to 4.0°C increase in temps over this century. Future rates of emissions (and thus temps) depend on economic development.

Global Climate Change What does a 1.8°C–4.0°C change mean for biological communities? Similar to elevational climate variation. The median value of change (2.9°C) = 500 m shift in elevation.

Figure Plants Are Moving Up the Alps (Part 1)

Figure Plants Are Moving Up the Alps (Part 2)

Acid and Nitrogen Deposition Sulfuric acid (H 2 SO 4 ) originates from SO 2 Nitric acid (HNO 3 ) from NO x. Carbonic acid (CO 3 ) from H 2 CO 3. Concept 24.3: Anthropogenic emissions of sulfur and nitrogen cause acid deposition, alter soil chemistry, and affect the health of ecosystems.

Acid and Nitrogen Deposition These acids can fall to Earth with precipitation (wet deposition) or with dust or aerosols (dry deposition). Natural precipitation has a pH of 5.0 to 5.6. Acid precipitation has a pH range from 5.0 to 2.0.

Figure Air Pollution Has Damaged European Forests

Figure Decreases in Acid Precipitation

Acid and Nitrogen Deposition Other problems with N deposition: Higher levels of NH 4 + and NO 3 – in soils lead to higher rates of microbial processes (nitrification and denitrification) that release N 2 O, a potent greenhouse gas.

Acid and Nitrogen Deposition N export to marine ecosystems can contribute to eutrophication and oxygen depletion. Anoxic conditions over large areas are called “dead zones.”

Atmospheric Ozone In the upper atmosphere (stratosphere), ozone provides a shield that protects Earth from harmful radiation. In the lower atmosphere (troposphere), ozone can harm organisms. Concept 24.4: Losses of ozone in the stratosphere and increases in ozone in the troposphere each pose risks to organisms.

Figure The Antarctic Ozone Hole (Part 1)

Figure The Antarctic Ozone Hole (Part 2)

Atmospheric Ozone An ozone hole is not really a hole, but an area with low ozone concentrations. In the Arctic, the decreases have not been as great (the Arctic ozone dent).

Atmospheric Ozone The Montreal Protocol has been signed by more than 150 countries, and went into effect in Concentrations of most CFCs have decreased, or remained the same. Recovery of the ozone layer is expected to take decades due to the long life of CFCs, and slow mixing of the troposphere and stratosphere.